Abstract
Plasma-assisted catalysis is an emerging technology for the atmospheric pressure and low bulk gas temperature synthesis of ammonia from molecular nitrogen and hydrogen. Direct evidence for plasma-induced surface reaction intermediates relevant to ammonia production, including surface hydrides and NHx (x = 1, 2, 3) species, has remained elusive. Here we report inelastic neutron scattering (INS) observations of alumina-supported Ni particles after treatment with N2 and H2 plasmas. INS experiments reveal the presence of NHx species and hydrides on Ni sites after exposure to sequential N2 and H2 plasma treatments. By separating exposure, we exclude the presence of plasma-phase reactions and demonstrate that these species are generated through plasma-facilitated surface reactions. INS spectra obtained from first-principles of NH3, NH2, and NH adsorbates on Ni support the experimental assignments of surface intermediates. The results directly implicate plasma stimulation of dinitrogen in generation of surface-bound nitrogen that participates in further hydrogenation reactions driven either thermally or with H2 plasma.
| Original language | English |
|---|---|
| Pages (from-to) | 2048-2053 |
| Number of pages | 6 |
| Journal | ACS Energy Letters |
| Volume | 6 |
| Issue number | 6 |
| DOIs | |
| State | Published - Jun 11 2021 |
Funding
A portion of this research used resources at the High Flux Isotope Reactor and/or Spallation Neutron Source, a DOE Office of Science User Facility operated by the Oak Ridge National Laboratory (Beamtime Proposals IPTS-20620.1 and IPTS-22959.1). The authors acknowledge partial support from the Air Force Office of Scientific Research under Award FA9550-18-1-0157 and the Department of Energy under Award DE-SC0021107. Z.W. was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Chemical Sciences, Geosciences, and Biosciences Division, Catalysis Science program. We thank the ND Energy Materials Characterization Facility (MCF) for the use of the D8 Advance Davinci, Bruker powder x-ray diffraction, and the Notre Dame Integrated Imaging Facility for access to the TEM. We also thank Audrey Miles for assisting in creating the Schrödinger equation solver used to compute the anharmonic frequencies. The MCF is funded by the Sustainable Energy Initiative (SEI), which is part of the Center for Sustainable Energy at Notre Dame (ND Energy).